An engine of a hybrid vehicle may be repeatedly stopped and restarted during the course of a trip to conserve fuel. Stopping the engine may increase vehicle fuel economy when the vehicle can be propelled by an alternative power source that does not solely rely on a hydrocarbon fuel. However, engine emissions may increase when the engine is restarted and powertrain torque may be limited until the engine reaches operating speed. Therefore, it may be desirable to provide a way to improve engine starting so that engine emissions are reduced and so that engine torque is available shortly after engine starting.
The inventors herein have recognized the above-mentioned issues and have developed a method for stopping an engine, comprising: adjusting a disconnect clutch application force in response to an engine stop request, and further adjusting the disconnect clutch slip to stop the engine at a desired position.
By adjusting operation of a driveline disconnect clutch in response to an engine stop request, it may be possible to position the engine during stopping so that fewer engine emissions are produced during engine starting. Additionally, the engine may be able to reach conditions where engine torque is available to the driveline in a shorter amount of time since the engine was stopped. In one example, a selected cylinder of an engine is stopped at a position a predetermined interval after top-dead-center (TDC) compression stroke of the cylinder and before the cylinder enters an exhaust stroke. Stopping the engine at this location allows spark and fuel to be injected to the cylinder in response to an engine start request so that combustion may be provided in the cylinder before engine rotation or shortly after engine rotation begins. As a result, the engine may reach operating speed sooner and less cylinder contents may be pumped to atmosphere before being combusted.
The present description may provide several advantages. Specifically, the approach may reduce engine starting time. Additionally, the approach may reduce engine emissions by pumping less cylinder contents to atmosphere. Further, engine starting time may be more repeatable.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.